Containers can be used to carry bulk materials, for instance raw building materials. However, one problem with this is that such materials are not always easy to unload. The containers tend to be tipped up from one end, so that the materials fall out of the other. However, this is not just a simple matter of tipping by a few degrees. Some materials require a tipping angle of over 45° to be fully unloaded. This requires tipping equipment and space and moreover can cause a lot of dust and mess.
An alternative to using a normal box container is to use a tank or silo container (with the tank in a container frame). The materials there are emptied through valves at the base. Whilst this may work for dry materials, it tends not to work for damp ones; the valves clog up.
The transportation of bulk materials is well exemplified by concrete. Concrete is a common construction materials and is a composite of cement, sand, gravel and water. The strength of cured concrete depends on the proportions of each component. Additives may be added to improve the fluid properties of the concrete during mixing and/or casting; others may be added to improve the hardness of the concrete after curing; colour pigments can also be added to give the concrete a distinct colour for a specific application, such as to differentiate the floor areas at a factory.
These raw materials are normally supplied in bulk by separate suppliers. For example, cement is manufactured only at a specialised plant, where limestone and large electric power are readily available and only at the locations approved by the environmental authorities. Similarly, gravels are produced at the quarries and the industry is also controlled by the environmental authorities. Sand may be dredged out from the sea or river bed. These raw materials are then transported to a batching plant. This may be at a construction site, but in many cases, there is no land available for an on site concrete batching plant or there may be other reasons why it is not feasible. In such cases, the raw materials are batched at a remote batching plant and transported to site by concrete mixers. This remote batching plant may have to occupy a large piece of land to stockpile the raw materials. In land-scarce countries, such as in Singapore, efficient use of land is a concern.
In many places, all the raw building materials are imported from the surrounding regions; gravel may come from one place with sand and cement coming from again different places. Typically, gravel and sand are transported by barges, while cement by specialised ship. At the landing point, these materials are stockpiled and then transferred to the batching plants or construction sites.
These batching plants and landing points are normally open facilities and the transfer of huge amounts of materials generates a lot of dust into the air. Abatement of dust pollution is therefore important.
Tipping of a container mounted on a truck tends to cause a lot of dust. Also tipping of a container suspended on a crane is not a safe practice. Shipping of wet sand and gravels in silo or tank containers does not work.
These problems necessitate a search for simpler and economical means of shipping and transfer of bulk materials and yet reducing pollution from the present levels.